1. Technical Field of the Invention
The present invention relates to a crimp terminal which is crimped to an end of a wire provided on an automobile or the like, a terminal-provided wire including the crimp terminal, and a manufacturing method thereof.
2. Description of the Related Art
To attach a terminal to an end of an insulated wire, there is conventionally often used a crimping technique. The crimping is performed by caulking a conductor barrel formed in advance on the terminal onto the end of a conductor of the insulated wire by use of a die.
This crimping technique, however, involves a difficulty of setting a crimp height of the conductor barrel. A low crimp height has a merit of lowering contact resistance between the conductor barrel and the conductor because the compression ratio of the conductor (a ratio between a sectional area of the conductor before crimping and that after crimping) is lowered, or in other words, crimping is performed with a high compression of the conductor, while causing a demerit of decreasing mechanical strength, in particular tensile strength against an impact load (more specifically, the holding strength by which the crimp terminal holds the wire), because of a high reduction rate of the conductor sectional area. On contrary, a high crimp height has a merit of maintaining high mechanical strength by securing a high compression ratio, that is, by suppressing a degree of the conductor compression, while raising the contact resistance between the conductor barrel and the conductor of the wire.
For solving the problem, as disclosed in Patent Document 1, for example, there is well known a conventional technique for increasing the strength with which the terminal holds the wire and effectively lowering the contact resistance: the technique includes forming a serration of a plurality of recessed grooves arranged in a parallel direction to an axial direction on an inner surface of a wire crimp portion of the crimp terminal, which surface is caulked to the conductor on the end of the wire. The serration increases a contact area between the wire crimp portion of the crimp terminal and the conductor. Furthermore, edges of the serration, particularly edges extending orthogonally to a terminal axis direction, cut into the conductor, thereby increasing the holding strength of the conductor by the wire crimp portion and lowering the contact resistance.
This technique of forming recessed grooves, however, has the other following problems.
Depending on the type of the wire onto which the crimp terminal is crimped, it may be required to set the compression ratio of the conductor due to crimping low to more highly compress the conductor. For example, in the case of the conductor formed of aluminum or aluminum alloy, on the surface of which an oxide film that will be a factor of deteriorating contact resistance tends to be formed, there is required to perform a high compression by setting the crimp height considerably lower than the case of the conductor formed by, for example, copper or copper alloy, in order to lower the contact resistance sufficiently against the oxide film.
Thus crimping with a high compression involves marked plastic deformation of the terminal crimp portion in the crimp terminal (in particular, axial stretch and thickness reduction). Accordingly, crimping the terminal crimp portion forming the recessed grooves described above may involves breaking the part forming the recessed grooves, that is, the part having a locally small thickness. This means that forming a recessed portion such as a serration in the terminal crimp portion will be extremely limited to a minimum of the compression ratio of the crimping, that is, a delimitation of the high compression. Patent Document 1: Japanese Patent Application Publication No. H10-125362